In telecommunication, a new technology called LTE-U (Long Term Evolution in Unlicensed) is being developed, where an LTE system can be applied to other frequencies than standardised in 3GPP (3rd Generation Partnership Project) standards.
For instance, LTE-U can be deployed to use the 5 GHz band, which is currently used mostly for WiFi. For instance, LTE-U can be used to deploy LTE as Supplemental Downlink (SDL), with the PCell (Primary Cell) always operating on a carrier in a licensed band.
However, since the 5 GHz band is unlicensed, there can be a lot of interference.